1. Field of the Invention
The present invention relates to a near-field optical recording apparatus which records information in a recording medium by utilizing near-field light emitted from a micro-aperture probe. The present invention also relates to a near-field optical recording and regenerating apparatus which records information in a recording medium and reading the recorded information by utilizing near-field light emitted from a micro-aperture probe.
2. Description of the Related Art
Conventionally, a near-field scanning optical microscope such as the photon scanning tunnelling microscope is known as an apparatus enabling analysis of shapes and structures of a specimen, which are smaller than a wavelength of light. The near-field scanning optical microscope emits near-field (evanescent field) light from a micro-aperture probe, and detects intensity of scattered light generated by interaction of the near-field light with a surface of a specimen, i.e., by disturbance of the near-field light by the surface of the specimen. The near-field scanning optical microscope scans the surface of the specimen with the micro-aperture probe and time-sequentially obtains a scattered-light-intensity detection signal as a function of the position of the micro-aperture probe. Thus, information on the shapes and structures of the surface of the specimen is obtained.
The above micro-aperture probe is usually produced by tapering an end portion of an optical fiber, forming a metal film by vapor deposition, and then removing the tip portion of the metal film to produce an aperture.
As an application of the above near-field scanning optical microscope, an apparatus for recording information in a recording medium by utilizing near-field light radiated from a micro-aperture probe is proposed. Although the power of the near-field light radiated from the micro-aperture probe is very small, the power density is considerably great. Therefore, it is possible to utilize a heating effect of the near-field light to produce a hole on a surface of ablative material or change the phase of phase-change material, for example, from a crystal phase to an amorphous phase. Since the near-field light is radiated from the micro aperture of a size smaller than a wavelength of light, it is possible to form as a pit a hole or an amorphous area having a size smaller than the wavelength of light, regardless of the diffraction limit of the light. Thus, recording with extremely high density is realized.
When reading the recorded information, the pit formed as above can also be read by utilizing the micro-aperture probe. For example, a hole formed in ablative material can be detected by adopting the aforementioned technique for measuring the fine shapes in the near-field scanning optical microscope. Therefore, a near-field optical recording and regenerating apparatus having the above micro-aperture probe for recording and reading information is proposed.
In order to achieve high reliability in the recording operation by the above near-field optical recording apparatus and near-field optical recording and regenerating apparatus, it is necessary to increase the power of the near-field light to a sufficient value which enables formation of a satisfactory pit realized by a hole or amorphous area. Although the power can be increased by supplying a sufficiently high power to the micro-aperture probe, the micro-aperture probe is liable to break when the power of the near-field light is increased.
The object of the present invention is to provide a near-field optical recording apparatus or a near-field optical recording and regenerating apparatus which forms a satisfactory pit so as to enable highly reliable recording even when the power of the near-field light is low.
In order to accomplish the above-mentioned object, according to the first aspect of the present invention, there is provided a near-field optical recording apparatus recording information in a recording medium. The near-field optical recording apparatus contains a light source which generates recording light; a micro-aperture probe which has at an end thereof a light-pass aperture having a diameter smaller than a wavelength of the recording light, receives from the other end thereof the recording light, and radiates near-field light on a portion of the recording medium to record the information; and an assistive heating unit which assistively heats at least the above portion of the recording medium for a duration corresponding to radiation of the near-field light on the portion.
In order to accomplish the above-mentioned object, according to the second aspect of the present invention, there is provided a near-field optical recording and regenerating apparatus for recording information in a recording medium, and reading the information recorded in the recording medium. The near-field optical recording and regenerating apparatus contains a light source which generates recording light; a micro-aperture probe which has at an end thereof a light-pass aperture having a diameter smaller than a wavelength of the recording light, receives from the other end thereof the recording light, and radiates near-field light on a portion of the recording medium to record and read the information; an assistive heating unit which is capable of assistively heating at least the above portion of the recording medium for a duration corresponding to radiation of the near-field light on the portion; and a control unit which activates the assistive heating unit when recording the information, and deactivates the assistive heating unit when reading the information.
In the first and second aspects of the present invention, the above duration corresponding to radiation may include a time preceding the radiation of the near-field light on the portion. That is, the above heating operation may be performed before the radiation of the near-field light on the portion.
Alternatively, in the first and second aspects of the present invention, the above duration corresponding to radiation may include a duration of radiation of the near-field light on the portion. That is, the above heating operation may be performed at the same time as the radiation of the near-field light on the portion.
Since, according to the present invention, the radiated portion is assistively heated for a duration corresponding to the radiation, both the energy of the assistive heating and the energy of the near-field light contribute to the recording. Therefore, even when the power of the near-field light is low, a satisfactory pit can be formed to enable highly reliable recording.
Generally, when recording information in a recording medium by radiation of light on the recording medium which is made of an ablative or phase-change material, and reading the recorded information therefrom, energy needed for reading the recorded information is smaller than energy needed for recording the information. Since, according to the present invention, the assistive heating unit is activated at least during the recording operation, and deactivated during the reading operation, it is not necessary to change the intensity of the near-field light. That is, even when the intensity of the near-field light is maintained so as to be constant, the energy supplied to a portion of the recording medium for reading the recorded information can be made smaller than the total energy supplied to a portion of the recording medium for recording the information.